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Published byJuliana Andrews Modified over 6 years ago
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SUBTROPICAL ANTICYCLONES AND RESULTANT WEATHER OVER SOUTH AFRICA
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Major Factors Influencing South Africa’s Climate
Ocean currents Altitude of the plateau High pressure systems SAA SIA KHP -n
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1. Ocean Currents
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2. Altitude of the Plateau
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3. High Pressure Systems
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THE IMPACT OF THE ANTICYCLONES
Kalahari HP SIA SAA
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SOUTH ATLANTIC ANTICYCLONE
Semi- permanent and semi-stationary feature Changes are seasonal – linked to the seasonal shift of the ITCZ and changes in surface temperatures Clear, stable weather Air moves anticlockwise around the system Cool, dry air moves onto the western and southern coasts of SA May deflect mid-latitude cyclones away or towards the coast. When ridges behind a cold front, weather along that front will intensify
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SOUTH INDIAN ANTICYCLONE
Semi-permanent and semi-stationary Air moves anticlockwise around the system and feeds warm, moist air into SA from the north-east When the system is located close to SA, there is a greater chance of moist winds reaching the western part of the country
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Kalahari anticyclone Over the interior, especially during the winter months (in reality it is part of the SAA and SIA) More intense during winter and weakens in summer
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In WINTER MONTHS Temperatures are lower, cool, dense air sinks onto the interior As the air sinks it is compressed and heated adiabatically It causes the lower layers to be warmer than those above them and an inversion is formed As a result of the air sinking, the pressure system ’rests’ on the escarpment. It acts as a lid and prevents warm, moist air moving from the Indian Ocean into the interior It causes the interior to experience dry winters
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In SUMMER Air is warmer and the system is less intense Inversion occurs above the level of the escarpment Thermal lows that develop in the interior also causes the inversion to occur at a higher altitude Moist air from the Indian Ocean can flow into the interior . This results in summer rainfall
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SEASONAL WEATHER AND CLIMATE CONDITIONS IN SOUTH AFRICA
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Line Thunderstorms
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LINE THUNDERSTORMS - SUMMER
MOI STURE FRONT Cold Benguela Warm Mozambique WARM MOIST AIR COLD DRY AIR H H
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Berg Winds
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High pressure in interior
SOUTH AFRICAN BERGWIND Anti clockwise circulation H High pressure in interior Danger: Veldfires Descending air heated Warm dry wind at coast L Low pressure over sea
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Synoptic Chart Revision
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It is a Winter chart if… Date (April – August)
Low temperatures over interior (use examples) Low dew point temperatures in interior – dry air Little or no cloud cover over interior (PTA) Cloud cover and rain over Cape Town – Mediterranean Climate Berg wind conditions – Pre frontal/coastal LP Cold front over interior No Tropical Cyclones High Pressure over interior
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Winter
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WINTER WEATHER MAP NO RAIN/CLOUDS KALAHARI HD LOW TEMP M.L. CYCLONE
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It is a Summer chart if… Date (October – February)
High temperatures over interior Dew point and maximum temperatures in interior within 5 degrees of each other – moist air Cloud cover over interior Little or no cloud cover and rain over Cape Town – Mediterranean Climate No cold front over interior Presence of a tropical cyclone Low Pressure over interior
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Summer
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SUMMER WEATHER MAP HIGH TEMP. TROPICAL CYCLONE NO KALAHARI HP
CLOUD COVER THUNDER STORM CYCLONES SOUTH HIGH TEMP. HIGH PRESSURES FURTHER SOUTH
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